Running two devices from OBDII port??

macoombi

Veteran Member
Joined
Mar 1, 2011
Location
Ottawa, Ontario, Canada
TDI
'02 Jetta TDI
Anyone tried using a y-splitter cable on the OBDII port to run two devices at the same time?

I've got a new insurance nanny device and I'd like to run something like a scangauge or Car Chip at the same time. Wonder if this is possible on my '02?
 

vw_norm

Gone, but not forgotten.
Joined
Jul 22, 2012
Location
Hawaii
TDI
2012 NMS TDI SEL Platinum Gray w/moonrock
Seconded. Run my scan gage and VCDS using a Y cable. I think those nannies just pull power. Take a look at how many pins it has. if only 2, its power. I doubt it 'speaks' german.
 

9mmkungfu

Veteran Member
Joined
Feb 3, 2012
Location
Virginia
TDI
2010 Jetta SportWagen, 2006 Jetta
I'm confused. This thread says yes it's fine. The linked thread says no it's not fine.
 

FlyTDI Guy

Top Post Dawg
Joined
Nov 3, 2001
Location
PNW
TDI
'01 Jetta GLS
It doesn't work for me... well kind of. I run SGII full time and was tired of having to unplug it for the sake of VCDS. Also, the SGII connector was a little fiddly to get on/off sometimes. I ended up getting a Y-Cord and it appears only one device can grab the line at a time, for me anyways. Whether the car's running or not, plugging VCDS into the 2nd port results in one of the two working, the other not. I can 'steal' the port from SGII using VCDS setup menu by testing the connection then saving but only sometimes. Other times it may take a couple tries. SGII will go blank when successful.

KWP protocols are pretty timing sensitive and if two devices are bombarding the ECU w/requests, things could get messy. Both devices will get all requested data regardless. When done, unplugging VCDS does not restore the display on SGII. I have to hit the menu button on SGII and then it re-establishes communication without further fiddling.

Dunno if CANBUS will handle this better. Could be on later model VW's two or more devices could play together just fine. Not so much on my older Mk4.
 
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JSWTDI09

Top Post Dawg
Joined
Jan 31, 2009
Location
Las Vegas, Nevada
TDI
2009 JSW TDI (gone but not forgotten)
Here is the issue. All OBDII communications must go through the CAN gateway. The CAN gateway can only handle one instruction at a time. It is possible to plug 2 devices into the connector with a "Y" cable. However, there will be problems if both devices try to talk to the car at the exact same time. The CAN gateway has no way to know that there are 2 devices, so it cannot address only one to send data to only one device. As long as one of the 2 devices is relatively quiet (not constantly demanding info), both devices will probably work OK. However, if one of the devices is polling for data constantly (like the Torque App running 6 gauges), I would not expect any other device to reliably communicate.

In other words, 2 devices can be plugged in at the same time, but they might not both work as intended. For any important function, I would not recommend plugging 2 devices in at the same time.

Have Fun!

Don
 
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